1. Field of the Invention
The present invention relates to the manufacture of heat exchangers and the manufacture of fins for heat exchanger cores primarily used in motor vehicles.
2. Description of Related Art
In the manufacturing of cores for motor vehicle radiators, charge air coolers and other air-cooled heat exchangers, serpentine fins formed from thin gauge metal strip such as copper or aluminum are placed between and in contact with the tubes which carry the fluid to be cooled. The heat exchanger core tubes typically extend between the manifolds, or the inlet and outlet tanks, of the heat exchanger. The fins are the chief heat exchange medium between the coolant and the ambient air. The ability of the fins to transfer heat from the tubes to the air passing over the fins greatly relies on the design of the fins, with some including dimples or protrusions to aid in the heat transfer. To increase the heat transfer rate even further, louvers have been incorporated into the fins. The louvers turbulate the air in a manner which has been found to increase the efficiency of the radiator. The louver configuration may be so-called full louvers, where each louver in the row extends over essentially the entire distance between the tubes, or split louvers, where two side-by-side banks of louvers are employed in the row, so that each of the two louvers extends over less than half of the distance between each tube.
Many heat exchangers employ such serpentine fins, in which a flat metal strip is folded into convolutions to create the multiple fins between spaced tubes. When louvers are incorporated into the fins, the structural integrity of the fin is compromised. Reinforcements to serpentine heat exchanger fins have been described in U.S. Pat. No. 5,361,829 to Kreutzer et al and U.S. Pat. No. 6,918,432 to Ozaki, as well as in U.S. Pat. No. 7,866,042 entitled “Method for Producing a Split Louver Heat Exchanger Fin” by this inventor, which application is hereby incorporated by reference. Such reinforcements have been added to serpentine fins for several reasons. The first, as stated by Kreutzer, is to provide support for flat heat exchanger tubes against bulging due to internal pressure. A second reason, as stated by Ozaki, is to prevent distortion of the fins during washing of the core with water at high pressure. A third reason, as stated by this inventor in U.S. Pat. No. 7,866,042, is to allow air forming of louvered serpentine fins. Additionally, serpentine fins are subject to compressive forces during the heat exchanger manufacturing operation of stacking the fins and tubes to make a core assembly. The stacked assembly of fins and tubes is held clamped under pressure during the subsequent soldering or brazing of the core. It has been found that the compressive strength of the serpentine fin is key to obtaining good fin-to-tube contact in the completed core. It has also been found that strengthening the front and rear face of the core by stiffening the leading and trailing edges of the fins provides protection to the core against damage due to handling during manufacturing, shipping and installation, as well as protection in service against damage due to road debris. All of these concerns are aggravated by the desire to use thinner fin materials to save weight and cost.